The subject matter disclosed herein relates generally to the detection of ionizing radiation, such as gamma-ray and X-ray radiation, and more particularly to scanning systems and methods of radiation detection, such as for medical diagnosis, using variable collimators, including Single Photon Emission Computed Tomography (SPECT).
Different scanning methods are known for use in detecting ionizing radiation, such as systems that use variable collimators, for example, adaptive collimators for Nuclear Medicine (NM) imaging. Some known methods of three dimensional (3D) image reconstruction use multiple image-acquisitions with different collimations of the imaging-collimator, such as by changing the collimation of the imaging-collimator. These systems use forward looking variable collimators constructed from multiple collimation elements where each collimation element may be varied and may produce multiple corresponding viewing-angles with a primary axis that is normal to imaging planes produced by detectors. These imaging planes are behind the collimators and are arranged to receive the radiation emitted from an imaged object via the collimators. The structures of the collimators and collimation elements are designed to reduce or avoid crosstalk of radiation between the collimation elements, for example, to prevent or reduce the likelihood of gamma rays passing through the gap of one septum into another collimator aperture.
The collimation variation in these systems is produced by changing the collimator height using means that move along a direction that is normal to the imaging plane while there is no relative movement between the collimator and the radiation detectors in a lateral direction, which is parallel to the imaging surface of the radiation detectors. However, in some situations, such a configuration may not be easy to implement and may increase the complexity of the system.
Additionally, the different viewing angles produced by the variable collimation elements are included in each other such that each viewing angle contains all the viewing angles that are smaller than this viewing angle. As a result, acquisition of multiple images using variable collimators of conventional systems creates a significant redundancy of information in which the same information appearing in one image appears in another image as well. In some of the images, the repeated information is the major information and only a small fraction of the information in these images is new information that does not appear in other images.
In order to increase the sensitivity of the imaging system, each of the multiple images acquired in different collimation of the imaging-collimator includes the imaged region. This imaged region is on and in the imaged object and is significantly larger than the size of the desired spatial resolution. The reconstruction of the image within the desired spatial resolution is produced by various image-reconstruction methods which include intensive mathematical calculations based on multiple equations that use image data from the multiple images. For example, in some systems, the number of images acquired for reconstructing a SPECT image times the number of pixels in each image is equal to the number of virtual voxels into which the imaged object is to be divided. Accordingly, the large size of the imaged region in each acquired image and the large number of acquired images that are needed for the 3D image reconstruction does not allow for selecting only images that have no information redundancy.
Thus, the reconstruction of images using some known systems and methods includes repetitive information that is summed with newly acquired information. As a result, reconstructed images may have reduced image quality and may also include reconstruction artifacts.